Add support accessing simple scalars (int32s, bools, and floats) in submessages

PiperOrigin-RevId: 566403598

rust/test/BUILD

@@ -298,3 +298,35 @@ rust_upb_proto_library(
     ],
     deps = [":reserved_proto"],
 )
+
+proto_library(
+    name = "nested_proto",
+    testonly = True,
+    srcs = ["nested.proto"],
+)
+
+cc_proto_library(
+    name = "nested_cc_proto",
+    testonly = True,
+    deps = [":nested_proto"],
+)
+
+rust_cc_proto_library(
+    name = "nested_cc_rust_proto",
+    testonly = True,
+    visibility = [
+        "//rust/test/cpp:__subpackages__",
+        "//rust/test/shared:__subpackages__",
+    ],
+    deps = [":nested_cc_proto"],
+)
+
+rust_upb_proto_library(
+    name = "nested_upb_rust_proto",
+    testonly = True,
+    visibility = [
+        "//rust/test/shared:__subpackages__",
+        "//rust/test/upb:__subpackages__",
+    ],
+    deps = [":nested_proto"],
+)

rust/test/nested.proto

@@ -0,0 +1,18 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2023 Google LLC.  All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd
+
+syntax = "proto2";
+
+package nest;
+
+message Outer {
+  message Inner {
+    optional int32 num = 1;
+    optional bool boolean = 2;
+  }
+  optional Inner inner = 1;
+}

rust/test/shared/BUILD

@@ -201,3 +201,17 @@ rust_test(
     ],
     deps = ["//rust/test:unittest_cc_rust_proto"],
 )
+
+rust_test(
+    name = "simple_nested_cpp_test",
+    srcs = ["simple_nested_test.rs"],
+    deps = ["//rust/test:nested_cc_rust_proto"],
+)
+
+# TODO(b/285309454): enable once we emit default messages for upb at the rust level
+# The default submsg that upb emits is NULL (whereas cpp returns a default constructed msg)
+#rust_test(
+#    name = "simple_nested_upb_test",
+#    srcs = ["simple_nested_test.rs"],
+#    deps = ["//rust/test:nested_upb_rust_proto"],
+#)

rust/test/shared/simple_nested_test.rs

@@ -0,0 +1,16 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2023 Google LLC.  All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd
+
+use nested_proto::nest::Outer;
+
+#[test]
+fn test_simple_nested_proto() {
+    let outer_msg = Outer::new();
+    // TODO(b/285309454): passing cpp, segfaulting upb
+    assert_eq!(outer_msg.inner().num(), 0);
+    assert!(!outer_msg.inner().boolean());
+}

src/google/protobuf/compiler/rust/message.cc

@@ -162,6 +162,38 @@ void MessageDrop(Context<Descriptor> msg) {
     unsafe { $delete_thunk$(self.inner.msg); }
   )rs");
 }
+
+// TODO(b/285309454): deferring on strings and bytes for now, eventually this
+// check will go away as we support more than just simple scalars
+bool IsSimpleScalar(FieldDescriptor::Type type) {
+  return type == FieldDescriptor::TYPE_DOUBLE ||
+         type == FieldDescriptor::TYPE_FLOAT ||
+         type == FieldDescriptor::TYPE_INT32 ||
+         type == FieldDescriptor::TYPE_INT64 ||
+         type == FieldDescriptor::TYPE_UINT32 ||
+         type == FieldDescriptor::TYPE_UINT64 ||
+         type == FieldDescriptor::TYPE_SINT32 ||
+         type == FieldDescriptor::TYPE_SINT64 ||
+         type == FieldDescriptor::TYPE_FIXED32 ||
+         type == FieldDescriptor::TYPE_FIXED64 ||
+         type == FieldDescriptor::TYPE_SFIXED32 ||
+         type == FieldDescriptor::TYPE_SFIXED64 ||
+         type == FieldDescriptor::TYPE_BOOL;
+}
+
+void GenerateSubView(Context<FieldDescriptor> field) {
+  field.Emit(
+      {
+          {"field", field.desc().name()},
+          {"getter_thunk", Thunk(field, "get")},
+          {"Scalar", PrimitiveRsTypeName(field.desc())},
+      },
+      R"rs(
+      pub fn r#$field$(&self) -> $Scalar$ { unsafe {
+        $getter_thunk$(self.msg)
+      } }
+    )rs");
+}
 }  // namespace
 
 void GenerateRs(Context<Descriptor> msg) {
@@ -246,6 +278,16 @@ void GenerateRs(Context<Descriptor> msg) {
                  }  // mod $Msg$_
                 )rs");
            }},
+          {"subviews",
+           [&] {
+             for (int i = 0; i < msg.desc().field_count(); ++i) {
+               auto field = msg.WithDesc(*msg.desc().field(i));
+               if (field.desc().is_repeated()) continue;
+               if (!IsSimpleScalar(field.desc().type())) continue;
+               GenerateSubView(field);
+               msg.printer().PrintRaw("\n");
+             }
+           }},
       },
       R"rs(
         #[allow(non_camel_case_types)]
@@ -279,6 +321,7 @@ void GenerateRs(Context<Descriptor> msg) {
           pub fn new(_private: $pbi$::Private, msg: $pbi$::RawMessage) -> Self {
             Self { msg, _phantom: std::marker::PhantomData }
           }
+          $subviews$
         }
 
         // SAFETY: